1. Field of the Invention
This invention relates to a device for detecting frosting for use, for example, in a refrigerator or a freezer.
2. Background of the Invention
In general, frosting occurs on the surface of the cooling fins or the like heat exchanger means of a refrigerator or a freezer. Such frosting on the cooling fins decreases cooling efficiency of the apparatus, and therefore timely defrosting is necessary for such apparatus. Theoretically speaking, the defrosting should preferably be made at a detection of the frost. In the prior art, such frost detection has been made by means of temperature difference between two point of the heat exchanger or by means of optical detection. The former method to detect the temperature difference has a shortcoming of producing erroneous signal under some ambient conditions especially under the influence of moisture, and the latter method utilizing optical method has a shortcoming that contamination of the optical system produces erroneous result. Another way of detecting a change of electrostatic capacitance or electric conductivity at frosting has been proposed, but errors caused by water produced by melted frost has not been avoided.
Accordingly, in the conventional refrigerators or freezer, in place of the actual detection of the frost on the heat exchanger, timer switches have been used to actuate defrosting system, such as defrosting heater or switching the circuit of cooling media to perform a defrosting. However, such timer-controlled system does not actually detect the frost. Therefore, when ambient moisture is extremely high, even in the timer-controlled period of defrosting interval, a considerable amount of frost grows on the heat exchanger hence decreasing cooling effect by the frost, or when the ambient moisture is considerably low, an unnecesssary defrosting is made when no frost grows on the heat exchanger thereby unnecessary raising the chamber temperature of the refrigerator or the freezer.